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ABSTRACT In the last few years, Digital Rock Physics (DRP) has become an avenue to investigate effective properties of geomaterials. In particular, the physical properties of samples imaged using micro-computed tomography (µCT) are estimated through segmentation of the µCT dataset. Nevertheless, segmentation proves to be a challenging and arbitrary procedure that might lead to inaccurate estimates of physical properties. Here we propose a new technique to extract elastic properties from a µCT dataset without the use of segmentation, thus improving accuracy and easing the overall workflow. The proposed method takes advantage of effective medium theories and uses the density and the porosity, which are measured in the laboratory, to constrain the final result. Presentation Date: Wednesday, October 19, 2016 Start Time: 9:15:00 AM Location: 167 Presentation Type: ORAL
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.49)
ABSTRACT Fractures play an important role in most carbonate and unconventional reservoirs. Traditional seismic methods for fracture identification and characterization are based on equivalent medium theory with the assumption that fracture dimensions and spacing are small relative to the seismic wavelength. Hence, the overall population of fractures is equivalent to a homogeneous anisotropic medium. However, effective medium models are not valid in highly heterogeneous media. Large fractures with spacing on the order of the seismic wavelength are more interesting because they are crucial for enhanced oil recovery, and they scatter seismic waves. To investigate the effect of realistic subsurface fractures on seismic waves, we model seismic wave propagation using an integral method with tetrahedral grid cells. The integral method is flexible in modeling irregular interfaces. It also has low computational cost and memory requirements, which is essential in 3D simulations. The fractures are explicitly treated as interfaces with displacement discontinuity using the linear slip model. We implemented the 3D explicit interface scheme on an irregular mesh. Arbitrary fractures are accurately modeled in the numerical discretization. Comparisons of seismic signatures induced by fractures with varying height, spacing, and density show significant differences in terms of scattering patterns. Relatively weak scattering patterns were observed with nonuniform distributions of fracture height and density. Constant fracture height and spacing tend to lead to strong scattering effects. Presentation Date: Wednesday, October 19, 2016 Start Time: 9:15:00 AM Location: 161 Presentation Type: ORAL
ABSTRACT The purpose of this work is to quantify the error in the match between a rock-physics model and well data and the error in the data. This process consists of a nonlinear least-squares fit of an appropriate rock-physics model to well data. Second, a repeat of the procedure includes systematic errors in the data, and the fit is redone for each value of data error. The result in the first case is a quantitative match between the model and the data. In the second case, a series or range of models results, with misfits for each case, as well as ranges of the output model parameters. This collection of models explains nearly all the error in brine-saturated data sands and approximately half of the data error in gas-saturated sands. The conclusions are that the two sources of error are quantified. This approach removes some subjectivity in the fit of a model to data, but the outputs can be monitored to ensure geologic plausibility. Presentation Date: Wednesday, October 19, 2016 Start Time: 3:10:00 PM Location: 167 Presentation Type: ORAL
- Geology > Geological Subdiscipline > Geomechanics (0.84)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.52)
ABSTRACT Most subsurface formations of interest sampled with sonic measurements are fluid saturated. When the sonic wave propagates in the formation, it induces pressure differences in the fluid on the order of a wavelength, which is explained by Biot's poroelastic wave theory. The sonic wave also induces pressure differences on the local scale due to the heterogeneity of the pores and pore shapes, referred to as squirt flow. In this work, we summarize a theory to investigate the combined effects that Biot and squirt flow have on the dispersion of the different sonic wave modes. We investigate an example of a fast formation with a permeable borehole wall using a monopole source although the theory also applies to mutipole sources such as dipole or quadrupoles. Our results show that squirt flow does not have a big impact on the Stoneley wave. However, we do find that the P and S-waves are relatively sensitive to squirt flow, whenever the frequency regime over which the squirt flow dispersion occurs is between 1-20kHz. Presentation Date: Tuesday, October 18, 2016 Start Time: 8:50:00 AM Location: 141 Presentation Type: ORAL
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Reservoir Description and Dynamics > Reservoir Fluid Dynamics > Flow in porous media (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Abstract High resolution, 3-D micro-structure images of rocks can be used to compute the transport and elastic properties of those samples using a digital rock physics approach. Those properties are complex functions of the pore size distribution, geometry and morphology, which necessitates the use of accurate 3-D volumes. Because of the limited availability of 3-D micro-structure images of rocks, several attempts to construct 3-D images from 2-D ones have been made. In this study, we propose a new stochastic method to reconstruct a 3-D image of the rock using only a 2-D section of the imaged rock sample. Our method is based on a simple observation that the pores are gradually deformed from one section to the next one. Therefore, the first step is to generate multiple independent realizations by performing Multiple-Point Statistics (MPS) based stochastic simulations. These simulations represent independent 2-D scans through the rock volume. Next, a succession of images is generated spanning two adjacent independent sections. These images consist of gradually morphed features from one section to those in the next independent section. Juxtaposing these 2-D images results in the reconstructed 3-D image. We calculate the spatial connectivity in the 3 direction and confirmed that the proposed method can retrieve the connectivity in the 3 direction accurately. We also compute transport and elastic properties from the reconstructed image and from the original image to verify that this method reproduces the appropriate spatial statistics and pore size distribution, geometry and morphology. We also compare the numerical results with laboratory measurements performed on the sample. The results obtained using the reconstructed image reveal that the numerically calculated properties are similar to the measured values. We compare the mismatch of transport and elastic properties with the original measurements with that of the previous reconstruction algorithm. These comparisons show that the proposed simulation method has the same accuracy as previous ones. However, the proposed method is much more computationally efficient than the other algorithms, mainly due to the faster MPS algorithm and the fact that the simulation is being done only for the independent layers instead of all the layers. The proposed methodology is an accurate method to reconstruct a 3-D representative sample of a rock given only one 2-D thin section. The algorithm is computationally efficient and faster than the previously introduced algorithm, and can easily be used to characterize samples for which 3-D images are difficult to obtain in terms of both time and expenses.